Periods Of Stasis Research Articles

Is Pinochet the Model?

Chileans are bemused by the attention paid the robust econ omy bequeathed them by General Augusto Pinochet. Reformers as far afield as Europe and America have taken special note of his reform of health care, education and social security. President Carlos Saul Menem pinned a medal on Pinochet, wishing aloud that he had received Argentina from his own democratically elected predecessor in as good political and economic condition. Most ironically, the one time Soviet Communist Party organ Pravda?which had led a worldwide campaign against the Chilean leader?interviewed to ask how Russia might follow the Chilean example. Indeed, the Pinochet is one of the standard cures touted for nearly any country seeking to make the transition from socialist poverty. This model, as it is widely understood, calls for some com bination of political repression and economic liberalism: a strong armed leader imposes a period of economic austerity and political stasis, after which the country emerges with a lean free-market econ omy, a vigorous civil society and a political class that is once again ready to assume the reins of government. The closer one looks, however, the more difficult it is to construe a model from Chile's experience. Chile's reforms are indeed admirable. But the path by which they were achieved is less so. Beyond its repressive, undemocratic nature, the military government

Musicology and Theory: Where It's Been, Where It's Going

Leonard Meyer theorized in 1967 that music composition in the West had entered a period of stasis: static because it no longer followed the largely singular, teleological path it had from the Renaissance through the early twentieth century, and fluctuating because it was marked by a myriad of movements and styles that operated largely independently of one another. The three most important of these independent movements were traditionalism (a relatively traditional approach to tonality and structure), analytic formalism (serialism and total serialism), and transcendental particularism (the attention to immediate sound particulars of aleatoric composition). These movements rise and fall in prominence, Meyer suggested, but create no metamovement, no overall sense of development, no common language. '

The role of gastric emptying in the absorption and metabolism of nifedipine given in a modified release pellet formulation

Abstract Plasma drug concentrations after a single oral administration of a modified release pellet formulation of nifedipine (20 mg) were measured in 18 healthy male volunteers after a light breakfast. The distribution of the radiolabelled pellets in the gastrointestinal tract was followed by gamma scintigraphy. The time for 50% gastric emptying ranged from 74 to 254 min (median 127 min), which is in good agreement with values reported for other multiparticulate formulations. In some subjects, periods of gastric stasis were observed, which may have been due to the inhibitory effect of nifedipine on gastric muscle contraction. Substantial spreading of the pellets occurred in both the small intestine and the colon, although in the majority of cases there was re-grouping at the ileo-caecal junction, prior to entry into the large bowel. The mean (±SD) C max was 36 ± 16 ng/ml (range 8.4–70.0 ng/ml), achieved 2–12 h post-dose (median t max 3 h). The pharmacokinetic data were consistent with twice daily dosage. Extended gastric residence may be an advantage for a modified release formulation. However, for nifedipine, a drug which undergoes a significant first-pass metabolism, slow gastric emptying may lead to a reduced systemic bioavailability as a result of the gradual presentation of the drug to enzymes on first pass through the intestine and liver.

Popular Protest and Political Reform in Africa

By the late 1980s, Africans joined the international clamor for democracy already ringing through eastern Europe, Latin America, and parts of Asia. While popular unrest had long been an intermittent feature of African politics, the collapse of the Berlin wall-and along with it Leninist one-party rule and the bipolar world order--inspired mass protesters and challenged incumbent leaders as never before. In and around 1990, citizens took to the streets of capital cities in some sixteen sub-Saharan African countries to express discontent with economic hardship and political repression and to demand civic reforms. Governments in the region faced pressures for political change on a scale unprecedented since the dissolution of colonial rule thirty years earlier. In response, between November 1989 and May 1991, at least twenty-one governments adopted significant reform measures to permit greater pluralism and competition within the polity. Multiparty elections were actually held for the first time in a generation in five African countries. Richard Sklar's daring prediction that Africans would come to prefer the vicissitudes of democracy to the stifling abuse of developmental dictatorships began to be brilliantly vindicated.' The dynamic process of protest and reform is nascent in Africa, and the future course of regime transitions is highly uncertain. But the moment is opportune to attempt a preliminary identification of emergent landmarks. Why have cracks appeared in the edifice of authoritarian rule in so many countries of the region? By what processes of struggle and accommodation is power being divided in monopolistic political systems? What are the prospects for the emergence and consolidation of democratic forms of governance? In the present paper we undertake three tasks. First, we catalogue the characteristics of recent political protests in sub-Saharan Africa, focusing on the turbulent spring of 1990. Second, we analyze the nature of government responses, noting the range of political reform initiatives undertaken by African leaders and recording backlashes, crackdowns, and reversals where they occurred. Finally, and most important, we seek to explain why the political firmament is shifting in Africa after a prolonged period of institutional stasis.

Influence of topical heparin on stasis-induced thrombosis of microvascular anastomoses.

An experiment was done to determine whether topical heparin and the association of anastomoses with dependent tissue (free flaps) exert any influences on stasis-induced microvascular thrombosis. Rat femoral vessel anastomoses with or without free flap construction were used in a total of 50 male Sprague-Dawley rats. Saline either with or without heparin was used for intralumenal irrigation during the anastomosis. Following anastomotic repair, the femoral vessels were reclamped, inducing stasis for either 2 or 4 hr. Our results showed that static blood had little adverse effect on thrombosis at the arterial anastomosis when reclamped for up to 4 hr in both standard and flap-associated anastomoses. Topical heparin significantly reduced the incidence of stasis-induced thrombosis of venous anastomoses. The venous patency rates in standard anastomoses were lower than those in flap-associated anastomoses after both 2 and 4 hr of stasis. From these results, we conclude the following. 1) Arteries may be reclamped for up to 4 hr without detriment despite static blood being in contact with the anastomotic site. 2) Topical heparin may be helpful in increasing the patency rate of venous anastomoses after a period of blood stasis. 3) Free flap construction may play a role in decreasing stasis-induced microvascular thrombosis.

RNA virus populations as quasispecies.

RNA virus mutation frequencies generally approach maximum tolerable levels, and create complex indeterminate quasispecies populations in infected hosts. This usually favors extreme rates of evolution, although periods of relative stasis or equilibrium, punctuated by rapid change may also occur (as for other life forms). Because complex quasispecies populations of RNA viruses arise probabilistically and differentially in every host, their compositions and exact roles in disease pathogenesis are indeterminate and their directions of evolution, and the nature and timing of "new" virus outbreaks are unpredictable.

RAPID EVOLUTION OF GASTRULATION MECHANISMS IN A SEA URCHIN WITH LECITHOTROPHIC LARVAE.

This study documents evolutionary modifications in mechanisms of gastrulation in Heliocidaris erythrogramma, an echinoid with lecithotrophic larvae. Radially symmetrical cell rearrangements and changes in cell shape drive elongation of the archenteron in the ancestral mode of echinoid gastrulation. Cell marking experiments indicate that in H. erythrogramma, however, prolonged movement of cells over the ventral lip of the blastopore accompanies extension of the archenteron. Evolutionary modifications to archenteron extension in H. erythrogramma thus include utilization of a different type of cellular movement as well as the imposition of dorsoventral asymmetry in cellular movements. The conservation of gastrulation mechanisms among phylogenetically divergent echinoids with planktotrophic development suggests that the plesiomorphic condition has persisted at least 250 million years and perhaps much longer. Yet H. erythrogramma diverged from an ancestor with planktotrophic development only about 10 mya, indicating that morphogenetic mechanisms of early development can undergo substantial evolutionary changes, even after long periods of stasis.

Sperm storage and degradation in the spermathecae of the salamander Eurycea Cirrigera.

Spermathecae are exocrine glands in the roof of the female cloaca that store sperm. Cytological and histochemical data indicate that the one type of secretion into the lumen is a glycoprotein. After a period of stasis in the summer, production of the secretion is initiated in the fall, coincident with an increase in ovarian follicular size. By the time of maximal follicular development and most intense mating activity in March and April, the spermathecal epithelium is filled with secretory granules. The secretory material is released into the lumen, enveloping the sperm. Many sperm remain in the spermathecae after oviposition, and most of these sperm are degraded in the spermathecal epithelium or pass through interruptions in the spermathecal walls caused by desquamation. Sperm in contact with the stromal environment are phagocytized by leukocytes. Some sperm, however, may survive in the lumen until at least the following fall. These sperm retain normal cytology, but whether or not they remain fertile and intact until a subsequent ovipository cycle is unknown.

CONTEMPORARY EVOLUTIONARY THEORY AS A NEW HEURISTIC MODEL FOR THE SOCIOSCIENTIFIC METHOD IN BIBLICAL STUDIES

Abstract. Notions of uniform and gradual evolution have been replaced in some circles by biological and paleontological models that postulate that periods of rapid change punctuate long periods of evolutionary stasis. This new theory, called punctuated equilibria (or PE for short), may have implications for paradigms in scholarly disciplines other than the sciences. Whereas old evolutionary models exerted great influence upon historians, sociologists, anthropologists, and students of religion for more than a century, the new model may provide heuristic paradigms for research that correlate more adequately with the current observations of scholars. We therefore provide suggestions for deployment of this new scientific paradigm in history and anthropology. In particular, this model can explain the rise of the Israelite state and the religious ethos in the Hebrew Bible, two major concerns of today's socioscientific study of biblical materials. Thus the possibility of an overarching paradigm for the social sciences is entertained.

Solubility in the rat lung of actinides associated with estuarine silt from West Cumbria

The solubility of actinides, associated with contaminated estuarine silt from West Cumbria, was measured in the rat lung. This material is similar mineralogically to airborne particles of silt involved in the sea-to-land transfer of radioactivity. A total of 25 mg of silt was administered to rats by multiple intratracheal instillations over a period of 7 weeks. There was no evidence of the rapid lung clearance phase normally observed in the rat and, after an initial period of stasis, most of the plutonium and americium was cleared from the lung with a half time of approximately 240 days. Some 15% of the retained plutonium isotopes and 10% of the 241Am were transferred to the skeleton over a period of about 3 months, indicating that both behave as ICRP Class W materials. Uptake by the liver was about 2% for both Pu and Am. Levels of actinides in the lung-associated lymph nodes were either at or blow the minimum level of detection. The significance of these results in relation to the ICRP lung model and to generalised derived limits for plutonium is discussed.

Patterns of evolutionary tempo and mode in the radiation ofMelanopsis(Gastropoda; Melanopsidae)

The Paratethyan basins of eastern Europe and western Asia became isolated from marine influence in the Late Miocene, and were the sites of several remarkable endemic radiations of brackish and freshwater organisms. Here I describe the patterns of tempo and mode before and during the radiation of the gastropodMelanopsisin the Pannonian basin of eastern and central Europe, and I explore the underlying mechanisms of evolutionary change.The most ancient melanopsid species in this area,M. impressa, was present in freshwater areas marginal to the basin well before the radiation. Widely spaced samples ofM. impressaindicate that this species underwent a period of stasis lasting at least 7 m.y. The end of stasis corresponded with the extinction of the last of the normal marine fauna in the basin, suggesting that the lack of other fauna and/or reduced salinity in the basin permitted expansion of the melanopsids from the basin margins into the basin proper. Stasis ended with the onset of changes in size, shouldering, and ontogeny, which led eventually toM. fossilis. Change occurred over a 2-m.y. interval; a series of intermediates is present for all three characters. Within-sample correlations provide no evidence that the three characters are constructionally linked; instead they appear to be changing independently. The mode of change in theM. impressa–M. fossilislineage appears to have been anagenetic. Alterations in the rate and direction of selection (and/or genetic links between characters) are probably required to explain the overall slowness of the change.Most Pannonian basin melanopsid species arose by rapid cladogenesis in the Middle Pannonian Stage. Physical factors in the basin probably influenced the timing of this diversification; contrasting patterns of variation and diversity between two melanopsid clades suggest that intrinsic factors influenced the extent of diversification.

The theory of punctuated equilibria and evolutionary anthropology

Abstract The impact of the theory of punctuated equilibria on anthropology is restricted to physical anthropology because, contrary to the situation in the nineteenth and early twentieth centuries, evolutionary theory now affects only this subdiscipline of anthropology. The major impact of punctuated equilibria theory occurs in palaeoanthropology. Here it affects discussion of rates of evolution, species discrimination in the fossil record, and species longevity and stasis. The principal palaeontological approach to species is to define them by morphological differences. This is a typological interpretation of species, because unvarying types are examined. Hence species are found to be separated by unbridgeable gaps, and the speciation event itself is all important. Emphasis on the speciation event explains why so many adherents of punctuated equilibria are also cladists. The strictly dichotomous branching of lineages and concomitant extinction of the ancestral species which occurs in cladistic analysis also emphasizes speciation. The generation and study of cladograms have become all important in palaeoanthropology, and the biology and adaptations of ancient hominids have been denigrated. Phyletic lines are dealt with as if they are the units of evolution, and not populations, as can be seen in a number of recent studies of Plio/Pleistocene hominids. Population thinking had been introduced into physical anthropology in 1951, and had caused the disappearance of both the degree of difference criterion for species and schemes of static human categories. Studies of fossil and living hominids were transformed. If studies of hominid adaptation and biology originate in the demise of typological thinking, they are endangered by the reintroduction of typological thinking by adherents of punctuated equilibria. Hominids are analysed in terms of migration and gene flow, and not in terms of adaptation to changing forces of natural selection and local population transformation in situ. Hence, for both fossil and living hominids, punctuated equilibria theory reintroduces catastrophism as an explanation for change. Some adherents of punctuated equilibria have denigrated sociobiology as a quest for generalizations about behavioral evolution among unnatural (non-cladistic, hence non-evolutionary) groupings of organisms not descended from a common ancestor, This may affect physical anthropologists who analyse human and non-human primate or mammalian behaviour and ecology from a sociobiological perspective. Archaeology is still another subdiscipline of anthropology which may be influenced by punctuated equilibria theory, although this is less certainly seen than in physical anthropology. It has been claimed, for example, that the archaeological record shows long periods of stasis and sudden, rapid bursts of change in stone tool industries, which is the principal evidence of behavioral evolution throughout most of hominid existence. Similar claims have been made for Egyptian cultural history. Archaeologists, however, have not accepted these generalizations. Yet one area in which punctuated equilibria theory does seem to have influenced archaeological interpretation lies in the analysis of Pleistocene and Holocene extinctions. Here the argument is that humans may have directly or indirectly contributed to the extinction of many animal species, perhaps in a catastrophic fashion.

Subunit interactions and physical properties of bovine gallbladder mucin

In this study the interaction of gallbladder mucin subunits was examined by gel permeation chromatography, quasielastic laser light scattering, and viscometry. Purified mucin eluted primarily in the void volume of a Sepharose 2B-Cl column, indicating a molecular weight above 2 × 106. Disaggregation of the mucin polymer resulted in the elution of glycoprotein in the included volume of the Sepharose 2B-Cl column. Gallbladder mucin had a hydrodynamic radius of 630 Å that was independent of mucin concentration below 2 mg/ml. At mucin concentrations above 2 mg/ml, a concentration-dependent increase in both hydrodynamic radius and apparent viscosity of gallbladder mucin was observed. Mucin demonstrated a strong pH dependence in hydrodynamic radius and viscosity with the maximum occurring at approximately pH 5.5. These findings suggest that noncovalent interactions participate in bovine gallbladder mucin subunit associations. Furthermore, changes that occur in the physicochemical environment of the gallbladder during periods of stasis may enhance the viscoelastic properties of mucin and promote the accumulation of biliary sludge in the gallbladder.

Effect of cardiac arrest time on cortical cerebral blood flow during subsequent standard external cardiopulmonary resuscitation in rabbits

Standard external cardiopulmonary resuscitation (SECPR) produces high cerebral venous and intracranial pressure peaks, low cerebral perfusion pressure, and low cerebral blood flow (CBF). Cerebral viability seems to require 20% of normal CBF, which SECPR cannot reliably generate. We tested the hypothesis that SECPR can produce adequate CBF if started immediately, but not if started after a long period of cardiac arrest (no flow, stasis). Cardiac arrest times of 1, 3, 5, 7 and 9 min were studied in rabbits. We measured unifocal cortical CBF with H2 clearance curves after saturation with H2 10%, O2 50% and N2O 40% by intermittent positive-pressure ventilation (IPPV). Measurements were made during spontaneous circulation (control condition), and then after resaturation immediately before induction of asystole by KCl i.v., and H2 clearance starting at end of arrest time during SECPR-basic life support with IPPV 100% and manual chest compressions (120/min) during asystole. Control cortical CBF was 30-40 ml/100 g brain per min. During asystole and SECPR, CBF greater than 20% normal was achieved only after no-flow of 1 min. After longer arrest (no-flow) times, CBF was less than 20% normal. Values were near zero after 7 and 9 min of cardiac arrest. Decrease in mean arterial pressures (MAP) produced by SECPR during asystole paralleled CBF values. Thus, the longer the preceding period of stasis, the lower the MAP and CBF generated by SECPR without epinephrine. This effect may be the result of anoxia-induced vasoparalysis and stasis-induced increased blood viscosity.

Sites and trend of erythropoiesis in anemic, normal, and splenectomized newts.

Newts, Triturus cristatus carnifex (Laurenti), were anesthetized by submersion in 2% chlorbutol in tap water for 15 min, splenectomized and then rendered totally anemic two months later by treatment with acetylphenylhydrazine (APH) diluted in their tanks (25 mg/liter for 36 h, changing the solution every 12 h). In the 14 weeks following hemolysis, erythron restoration occurred with the same intermittence as it did in whole animals rendered anemic by APH treatment: Beginning the second week the red blood cell count progressively increases for about one month, followed by a period of stasis which lasts about three weeks, then by a new increase, and then by a final period of stasis. Histological examination shows that erythropoietic activity occurs partly in the circulating blood and partly in erythroblasts nestled in the crypts between the muscular trabeculae of the ventricle as well as in the atrial walls. These cells, which are not part of the freely circulating elements in the blood stream, become very abundant in both whole and splenectomized anemic newts but are also present in normal animals. Newts, thus, have three sites for erythropoiesis: the spleen, the blood stream, and the heart. The other components compensate for the elimination of the spleen without determining any lack of, or delay in, erythropoietic response.

Patterns of evolution among lower Jurassic crinoids

The crinoid families Isocrinidae and Pentacrinitidae are well represented in the British Lower Jurassic, allowing a detailed investigation of their evolution at this time. The pseudopelagic pentacrinitids diverged from the benthic isocrinids during the Triassic. Seirocrinus arose from Pentacrinites through hyper‐morphosis prior to the start of the Jurassic but both genera subsequently show extreme evolutionary conservatism, perhaps attributable to constraints imposed by their unusual life‐style. From a single species in the Hettangian, the benthic isocrinids diversified in the Sinemurian and Carixian. A “central lineage”;, comprising three species of Chladocrinus, evolved along a peramorphocline by “intermittent anagenesis”;, prolonged periods of evolutionary stasis punctuated by short periods of gradualistic change. Two main offshoots, Balanocrinus and Hispidocrinus gen. nov., represent shifts into new habitats. Balanocrinus arose through progenesis, with subsequent evolution along a paedomorphocline, wh...

Cladogenetic and anagenetic changes in the morphology ofRhizosolenia praebergoniiMukhina

Biometric analysis of a late Pliocene planktic diatom morphospecies, Rhizosolenia praebergonii Mukhina, from the equatorial Pacific Ocean indicates that it represents a lineage which underwent relatively rapid change in morphology after its first appearance (3–1–2–7 Ma) followed by a period of time where the rate (as expressed as a slope) of morphological change was not significantly different from zero (2–7–1–7 Ma). Based on criteria for identifying ancestral‐descendant relationships (Prothero and Lazarus, 1980), we conclude that R. praebergonii evolved from R. bergonii Peragallo via a cladogenetic event. The observed pattern of evolution conforms to the shifting balance model of evolution, rather than to a punctuated model. Isotopic evidence suggests that paleoclimatic events may have played a role in the onset of the period of stasis.

Pseudosinella revisited (Collembola, Entomobryinae)

Eight controversies are active in the study of macroevolution. These are: 1) the meaning of the term macroevolution, 2) the role of chance, 3) the role of stasis and gradualism, 4) whether significant change is Iimited to speciation events, 5) the environmental conditions where macroevolutionary change occurs, 6) whether Neodarwinian mechanisms are adequate to explain change, 7) the existence and nature of hierarchical evolutìonary processes, and 8) Darwin’s views about all this. After a brief examination of each of these issues we used the extensive data available for 9 species of European and Nearctic cave Pseudosinella to examine the third, fourth and fifth controversies mentioned above. Our conclusions are that while we are unable to demonstrate ongoing directional selection, we have clear evidence that significant adaptive change is not limited to speciation events. It does however appear that the amount of adaptive change is greater in the process of speciation than in between. We also show that there is no evidence for clear periods of stasis in the evolution of these forms. This leads us to a new model of the macroevolutionary process combining features of gradualism and punctuated equilibrium. We also showed that evolutionary change is not associated with unstable environments but rather with more stable ones.

Periodic changes in the organs involved in the erythropoiesis of anemic newts.

In Triturus cristatus carnifex (Laurenti) newts rendered totally anemic by treatment with acetylphenylhydrazine (APH) diluted in their tank water (25 mg/liter for 48 hours, with four changes) the recovery of erythron occurs through periodic cycles of mitotic activity in the erythropoietic tissue. These cycles determine a marked increase in blood erythrocyte concentration at regular intervals of about 1 month. The consequence of this trend is the alternation of ferritin and hemosiderin accumulation phases during periods of stasis with iron mobilization phases during periods of erythropoietic activity, which is particularly evident in the Kupffer cells of the liver. Iron mobilization and erythropoietic activity are strictly related to the periodic hypertrophy of some Bowman's capsule cells in the renal corpuscle, which were previously denominated "lactate sensitive cells" (LSC). The histochemistry, location, and behavior of LSC indicate that they are probably the site of erythropoietin production in the newt.

The role of gradualism and punctuation in cave adaptation

The theory of punctuated equilibrium, offers a potential explanation for the profound morphological changes that accompany isolation in caves. I consider three aspects of punctuation theory: the association of morphological change with speciation; periods of stasis; and the number of genes controlling a trait. If the evolution of cave organisms is associated with speciation, then speciose groups and cave species derived from other cave-limited species should show increased adaptation. Analysis of Kane and Barr’s data on the subspecies of Neaphaenops tellkampfi and Holsinger’s data on crangonyctid amphipods fails to provide any support for the hypothesis. If the evolution is characterized by long periods of stasis, then directional selection should be rare. An estimate of selection in a cave population of Gammarus minus indicates that directional selection is occurring. Third, if punctuation is important, characters associated with isolation in caves should be controlled by a single gene. Wilkens and others have found most characters in cave Astyanax to be controlled by between 3 and 7 genes. It is more useful to frame the question of evolutionary change accompanying cave invasion in terms of adaptive topographies. Several examples of its use are discussed, including assessing the role in selection in structural reduction, and the role of isolation in adaptation to cave life.